Partial Payment Link – Blank Checkout?

Hi all

I’m having a bit of trouble with my site and I thought it best to turn to people who will know more about it than me!

Basically, I am using the WooCommerce Deposits/Partial Payments plugin, and when I send customers their partial payment link, the link is taking them to a blank checkout.

https://www.cherrytopweddings.com/df480-checkout/order-pay/4558/?pay_for_order=true&key=wc_order_OVFI7zi0hFL55&payment=second_payment

As far as I am aware, the link is structured as it should be, the only point to note being that this is the second payment for order #4556, so should it be 4556-2 in the URL?

I am using Sagepay/Opayo as the payment gateway.

Any help/ideas would be greatly appreciated.

The page I need help with: [log in to see the link]